Andrea Smith recently received a Facebook friend invitation from someone she went to junior high school with — 23 years ago.

“I found it kind of baffling,” said Smith, 38, of Ypsilanti, Mich. “I knew who she was, but I don’t recall that we were ever friends. I don’t recall that we ever had a conversation.”

Social networking sites such as Facebook have experienced phenomenal growth in the past year, according to market researcher comScore. Facebook is now the No. 1 social networking site, with more than 120 million active users, and its fastest growing demographic is those 25 and older.

But with so many opportunities these days to connect with people online, some are confronting a question they thought they had left behind during their awkward adolescent years: What if I don’t want to be your friend?

“It’s really odd when suddenly your past comes out and finds you,” said Troy Sandal, 38, of San Francisco, who says he’s been contacted recently by former high school classmates. His 20-year high school reunion was held over the summer, although he did not attend. “To be honest, I had two friends in high school and I kept in touch with one.”

Sandal, who’s been on Facebook for about two years, says he’s not interested in collecting a large number of online friends. “You don’t want to add them as friends, you want to add them as ‘Hey, I knew yous,’ ” he said.

OK to ignore an invitation
It’s perfectly OK to ignore an invitation, especially one the sender has made no effort to tailor specifically to you, said Jason Alba, CEO of JibberJobber.com and co-author of “I’m on Facebook — Now What???”

"You don’t have to respond to every single thing that comes at you," he writes.

Some users of social networking sites prefer to “friend” people who are colleagues or friends in real life. Some send invitations to friends of friends in an effort to expand their network, while others attempt to friend someone who has an interesting profile. Those new to Facebook are prompted to send a friend request to everyone in their address book (although they have the option to skip this step).

That’s what happened to Laura Hesse, 36, of Orange, Calif. When she signed up for Facebook in August, she had a friend talk her through the initial setup. In the process, she sent a mass invitation of friendship to everyone in her address book — including a family member she had cut all ties with.

“I had no idea what I was doing!” Hesse said. “I was like, ‘Oh my God, no, she’s going to get it!’ ”

“She was able to catch up on the past three or four months of my life,” said Hesse, including photos of her kids and a recent kitchen remodel. “I kind of felt like she got a whole glimpse of it within a few hours. There’s a reason they’re not in my life, and there’s a reason I didn’t want them to see this stuff.”

As soon as Hesse realized she could “unfriend” her family member — by clicking on the X to the right of her name — she did. Hesse then disappeared from her relative’s Facebook page, although she later heard the woman was devastated when she found out.

Social awkwardness
Such examples of social networking faux pas are nothing new to teenagers, who were first forced to figure out the boundaries of acceptable social behavior on MySpace a couple of years ago, said Danah Boyd, a fellow at the Harvard Berkman Center for Internet and Society.

“You go through a period of absolute social awkwardness,” she said, as every new wave of people to get connected works out social norms within the technology.

It’s all about dealing with expectations, said Ariel Waldman, community manager for Pownce, a social networking and microblogging site. “In Web 2.0, people have developed expectations of what friending or not friending means. They get put off if their expectations are not met.”

One person might want to follow only 200 people on Twitter, for example. Another might prefer to friend only those in the same geographic location.

“Everyone has different communication protocols,” Waldman said. “The important thing is defining what your own protocols are.”

Then there’s the issue of real friends versus online friends. Take Hal Niedzviecki of Toronto, who wrote about his experience throwing a “Facebook party” for the New York Times Sunday Magazine. He invited his nearly 700 online friends to meet him at the neighborhood bar. One showed up.

However, there are benefits to maintaining a large network of friends, said Nicole Ellison, an assistant professor in the Department of Telecommunication, Information Studies and Media at Michigan State University.

“People who are ‘weak ties’ (friends of friends) are more likely to be different from you and more likely to provide you with new information and different perspectives than your close friends,” she said. For example, you’re more likely to find a job lead from a friend of a friend.

Some opt to segment their social networking life by using LinkedIn for work associates and Facebook for close friends, although Ellison acknowledges that the lines between the two are not always so clearly drawn. She recommends using privacy settings to limit the kind of information certain groups on your network can see.

And that so-called “friend” you can do without?

“A user will not receive any notification that someone has ‘ignored’ their friend request,” said Facebook spokeswoman Stephanie Pettinati.

Smith, who was contacted by her former junior high school classmate, said she tries to limit her online friends to people she actually knows because of the personal details she posts on her Facebook page. “I try to keep the number of people who have access to that information to a minimum.”

As for the friend request? It’s still there on her Facebook page, unanswered.